The thin film transistor (TFT) is a key component in a liquid crystal display device, and plays very important function to working performance of the display device. The liquid crystal display device for example may comprise a liquid crystal display, and each liquid crystal pixel point on the liquid crystal display is driven by a TFT integrated behind it, so that the liquid crystal display can display screen information at a high speed, high brightness and high contrast.
In recent years, a copper thin film of low resistance has begun to be used on a semiconductor integrated circuit, electrodes and wirings of a thin film transistor. Since the resistance of copper is relatively low, it can increase communication speed of a digital signal and reduce power consumption. However, in the thin film transistor, the adhesion between an electrode thin film and an adjacent thin film layer is relatively bad, particularly the copper electrode thin film. In addition, atoms in the electrode thin film may diffuse into the thin film layer in contact with it, and influence the property of the adjacent thin film layer. For example: the adhesion between a source or drain containing copper and an active layer is relatively bad, and copper atoms in the source or drain containing copper may also diffuse into the active layer and influence the property of the active layer.
To sum up, in the thin film transistor of the prior art, the adhesion between the electrode thin film and the adjacent thin film layer is relatively bad, and the electrode thin film may also influence the property of the adjacent thin film layer.